We genotyped 6 tagging SNPs spanning GABRA2 and GABRG1 from among 13 previously identified SNPs in a sample of 380 AA subjects with AD and 253 AA control subjects. Although we did not find significant evidence for single SNP association with AD, haplotype-based analysis of GABRG1-GABRA2 showed promising results in both global and specific comparisons. There was evidence for haplotypic association with both genes, but the evidence for association with GABRA2 was much stronger than that for GABRG1. To investigate the interactions of multiple SNPs both within each gene and spanning both genes, haplotypes were reconstructed combining three SNPs for each gene separately and all six tagging SNPs together. Three-SNP haplotypes were reconstructed from SNPs A, D, and F to investigate the role of GABRG1. Three-SNP haplotypes containing SNPs G, J, and L were reconstructed for the GABRA2 analysis. A nominally significant difference was observed in the G1-4 haplotype (C-G-T in Table 2), which reflects the potential for a small role of GABRG1 in AD risk in AAs, but the difference in GABRA2 haplotype frequencies was much more statistically significant
